1. Field of the Invention
The present invention relates to a gallium nitride group compound semiconductor represented by a general formula AlxGayIn1-x-yN (0xe2x89xa6xxe2x89xa61, 0xe2x89xa6yxe2x89xa61, 0xe2x89xa6x+yxe2x89xa61), and to a method for manufacturing such a semiconductor. In particular, the present invention relates to a method for manufacturing a gallium nitride group compound semiconductor in which an epitaxial lateral overgrowth (ELO) method is used to form a layer on a substrate.
2. Description of the Related Art
A gallium nitride group compound semiconductor is a direct-transition-type semiconductor having a wide emission spectrum range from ultraviolet to red, and is applied to light-emitting devices such as light-emitting diodes (LEDs) and laser diodes (LDs). The gallium nitride group compound semiconductor is, in general, formed on a sapphire substrate.
However, in the above-described conventional technique, when a layer of a gallium nitride group compound semiconductor is formed on a sapphire substrate, a crack and/or warpage is generated in the semiconductor layer due to a difference in thermal expansion coefficient between sapphire and the gallium nitride group compound semiconductor, and dislocations are generated in the semiconductor layer due to misfit, resulting in degraded device characteristics.
Accordingly, in light of the above problems, an object of the present invention is to realize an efficient method capable of forming a layer of a gallium nitride group compound semiconductor without generation of cracks and dislocations to thereby improve device characteristics.
In order to solve the above problems, the present invention has a first feature that resides in a method for manufacturing a gallium nitride group compound semiconductor comprising the steps of growing a first gallium nitride group compound semiconductor on a substrate; etching the first gallium nitride group compound semiconductor into an island pattern such as a dot pattern, a striped pattern, or a grid pattern such that substrate-exposed portions are formed in a scattered manner; and growing a second gallium nitride group compound semiconductor which causes epitaxial growth from an island or islands of the first gallium nitride group compound semiconductor serving as nuclei (seeds) but which does not or hardly cause epitaxial growth from the substrate-exposed portions, so that the second gallium nitride group compound semiconductor is formed by lateral growth above the substrate-exposed portions.
The xe2x80x9clateralxe2x80x9d direction as used in the specification refers to a direction parallel to a surface of the substrate (surface direction).
By using the above-described method, the second gallium nitride group compound semiconductor does not grow on the substrate-exposed portions, but grows on the island(s) of the first compound semiconductor in a 3-dimensional manner, including growth in the surface direction. And on the upper surface of the substrate, the second gallium nitride group compound semiconductor grows uniformly. Accordingly, dislocations due to misfit between the substrate and the gallium nitride group compound semiconductor grow in the vertical direction, but not in the lateral direction. Consequently, no vertical through-dislocations are generated in the second gallium nitride group compound semiconductor above the substrate-exposed portions, and vertical through-dislocations are generated in portions of the second gallium nitride group compound semiconductor located above the island(s) of the first gallium nitride group compound semiconductor. As a result, the surface density of vertical through-dislocations in the second gallium nitride group compound semiconductor decreases significantly, resulting in improved crystallinity of the second gallium nitride group compound semiconductor. In addition, since there are no chemical junctions between the substrate-exposed portions and the layer of the second gallium nitride group compound semiconductor thereabove, the second gallium nitride group compound semiconductor causes neither warpage nor distortions which would otherwise be caused by stress in the layer.
A second feature of the present invention is that the substrate is made of sapphire, silicon, or silicon carbide. These materials improve the crystallinity of the second gallium nitride group compound semiconductor obtained on the substrate.
A third feature of the present invention is that the substrate is formed of silicon; the first gallium nitride group compound semiconductor formed in an island pattern is formed of a gallium nitride group compound semiconductor containing aluminum, and the second gallium nitride group compound semiconductor is formed of a gallium nitride group compound semiconductor containing no aluminum. The gallium nitride group compound semiconductor containing aluminum grows epitaxially on silicon, but the gallium nitride group compound semiconductor containing no aluminum does not grow epitaxially on silicon. Accordingly, it is possible to form island(s) of the first gallium nitride group compound semiconductor on a silicon substrate, and then form the second gallium nitride group compound semiconductor which grows epitaxially on the island(s) of the first gallium nitride group compound semiconductor but which does not or hardly grow epitaxially on the substrate-exposed portions. Consequently, above the substrate-exposed portions, the second Gallium nitride group compound semiconductor grows epitaxially in a lateral direction from the island(s) of the first gallium nitride group compound semiconductor serving as nuclei (seeds), so that a gallium nitride group compound semiconductor of high crystallinity can be obtained.